Modulation of Geraniol Metabolism During Alcohol Fermentation
Enrico Vaudano 1,2, Emilia Garcia Moruno 1 and Rocco Di Stefano 1
1 Istituto Sperimentale per l'Enologia, Via Pietro Micca 35, 14100 Asti, Italy.
2 Corresponding author. E-mail: enologia@tin.it and sezione.chimica@tin.it
J. Inst. Brew. 110(3), 213-219, 2004 | VIEW ARTICLE
ABSTRACT
Geraniol is the main monoterpenol present in Gewurtztraminer
white grapes and in some red aromatic grapes from
northern Italy. During fermentation, the geraniol
concentration showed a dramatic drop and a small
amount was transformed into linalool and α-terpineol
by an acid catalysed chemical reaction. Yeast are
responsible for changing most of the geraniol to
citronellol through enzymatic reactions. The final
aroma of wine is due mainly to both the untransformed
geraniol and the formed citronellol. In this study,
competition between the geraniol-citronellol transformation
and another metabolic process, in which according
to our hypothesis sterol biosynthesis is involved,
was investigated. Geraniol, in the active form of
geranyl pyrophosphate, is one of intermediates in
that metabolic pathway.
The addition of ergosterol, one of final products of sterol biosynthesis, to the fermentation medium, appeared to reduce the amount of geraniol involved in this metabolic pathway; as a result geraniol-citronellol transformation was favoured. The result was a higher production of citronellol with the same geraniol consumption. The relationships between oxygen and regulation of the metabolic pathways involving geraniol were also studied. Results showed that aerobic conditions could improve citronellol production. Finally, it was observed that metabolism of geraniol also depended on the physiological state of the yeast during fermentation.
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Publication no. G-2004-0810-226 ©2004 The Institute & Guild of Brewing